Abstract:

Objective To analyze the association between mtDNA mutations and photodamage after ultraviolet B （UVB） irradiation. Methods Primary human skin fibroblasts （HSF） and primary human epidermal keratinocytes of adult （HEKa） were irradiated by sub-lethal doses of UVB thrice a day for 4-5 days. Thereafter, genomic DNA was extracted from irradiated cells and conventional PCR was applied to detect the frequency rates of 4977 bp and 3895 bp mtDNA deletion. To quantitatively analyze the mutation levels, SYBR Green real-time PCR method was performed. Results In both cell lines, the frequency rates and relative copy number of deletions increased with the cumulative doses of UVB exposure （P < 0.05）. The prevalence rate of 3895 bp deletion peaked 53.3％ and and relative copy number reached （49.63 ± 4.38） × 10-5, showing a more intense response to the accumulation of UVB radiation than 4977 bp deletion. In HSF, the minimum cumulative dose of UVB radiation was 150 mJ/cm2 for the induction of 3895 bp deletion, and 200 mJ/cm2 for the induction of 4977 bp deletion. It seemed that mtDNA deletion was more readily to be induced by UVB radiation in HSF than in HEKa. Conclusions The development and accumulation of mtDNA mutation are intimately related with cumulated UVB dose received by skin cells, and the 3895 bp deletion is more reliable in monitoring the photodamage caused by UV than 4977 bp deletion. Therefore, the 3895 bp deletion may serve as a biomarker for the detection of photodamage in skin cells. HSF appear to have an increased susceptibility to UVB radiation, which results in a higher frequency and level of mtDNA mutations compared with HEKa.

Key words: Cellular aging;mitochondrial DNA;mutation